Swamp cooler
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Swamp coolers (also called "evaporative coolers") are air conditioners used to cool buildings in dry climates. The technique they use is evaporative cooling, of which two types exist: direct evaporative cooling and indirect evaporative cooling.
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Evaporative cooler designs
Direct Evaporative Cooling (open circuit)
- used to lower the temperature of air by using latent heat of evaporation, changing water to vapor. In this process, the energy in the air does not change. Warm dry air is changed to cool moist air. Heat in the air is used to evaporate water.
Indirect Evaporative Cooling (closed circuit)
- similar to direct evaporative cooling, lowers the temperature of air by using latent heat of evaporation via some type of heat exchanger. The cooled moist air never comes in direct contact with products or environment.
Typical
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Typically, residential and industrial swamp coolers use direct evaporative cooling and can be described as an enclosed, metal or plastic box with vented sides containing an axial fan (squirrel cage), fan motor with pulley wheels and a water pump to wet the cooling pads. They can be mounted on the roof (down draft) or exterior walls (side draft) of buildings. To cool, the fan draws ambient air through vents on the sides and through the damp pads. Heat in the air evaporates water from the pads which are constantly re-dampened to continue the cooling process. This cooled, moistened air is then delivered to the building via a vent in the roof or wall.
Because the cooling air originates outside the building, a vent must exist to allow air to move from inside to outside. Air should only be allowed to cycle once through the system or cooling efficiency will fail. This is due to the air reaching the saturation point.
Cooler pads
Traditionally, swamp cooler pads consist of aspen wood fiber inside a containment net, but more modern materials, such as some plastics and melamine paper, are entering use as cooler-pad media. Wood absorbs some of the water, which allows the wood fibers to cool passing air to a lower temperature than some synthetic materials. The thickness of the padding media plays a large part in cooling efficiency, allowing longer air contact. For example, an eight-inch-thick pad with its increased interface will be more efficient than a one-inch pad.
Evaporative (wet) cooling towers
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Cooling towers are larger structures for cooling water or other working medium to near-ambinet temperature. Wet cooling towers operate on the evaporative principle and may be used in a swamp cooling arrangement. Cooling towers can be found on large buildings or on industrial estates.
With respect to drawing air through the tower there are three types of cooling towers:
- natural draft, which utilizes a tall chimney,
- fan assisted natural draft, and
- mechanical draft which uses power driven fan motors to force or draw air through the tower.
If ambient conditions are right plumes (fog) can be seen rising out of evaporative (wet)cooling towers.
Misting systems
Misting system work by forcing water via a high pressure pump and tubing through a brass and stainless steel mist nozzle that has an orifice as size of about 5 micrometres producing a micro-fine mist. The water droplets that create the mist are so small, that it instantly flash evaporates. This flash evaporation can reduce the surrounding air as much as 35 °F in just seconds. For patio systems, it is ideal to mount the mist line approximately 8 to 10 feet above the ground for optimum cooling. Misting is used on for many different applications including orchids, pets, livestock, kennels, insect control, odor control, zoos, veterinary clinics, produce cooling, greenhouses, etc.
Performance
Understanding evaporative cooling performance requires an understanding of psychrometrics. Evaporative cooling performance is dynamic due to changes in external temperature and humidity level. Under typical operating conditions, an evaporative cooler will nearly always deliver air cooler than 80 °Fahrenheit (27 °Celsius). A typical residential swamp cooler in good working order should cool air to within 6°F - 8°F (3°C - 4°C) of the wet bulb temperature.
Some rough examples clarify this relationship.
- At 90 °F (32 °C) and 15% relative humidity, air may be cooled to nearly 60 °F (16 °C).
- At 90 °F (32 °C) and 50% relative humidity, air may be cooled to about 75 °F (24 °C).
- At 105 °F (40 °C) and 15% relative humidity, air may be cooled to nearly 70 ° (21 °C).
Because swamp coolers perform best in dry conditions, they are prevalent and most effective in arid, desert regions like the southwestern USA and northern Mexico.
(cooling examples extracted from the June 25, 2000 University of Idaho publication, "Homewise (http://info.ag.uidaho.edu/homewise/homewise_062500.htm)").
Advantages vs. refrigerated air-conditioning
Less expensive to install
- Estimated cost for installation is 1/8 to 1/2 that of refrigerated air conditioning
Less expensive to operate
- Estimated cost of operation is 1/4 that of refrigerated air.
- Power consumption is limited to the fan and water pump vs. compressors, pumps, and blowers.
Fresh air
- The constant stream of air from intake to vent through the building freshens the air in the building.
Disadvantages vs. refrigerated air-conditioning
Performance
- High temperature, high humidity outside conditions decrease the cooling capability of the swamp cooler.
Comfort
- The air supplied by the swamp cooler is nearly 100% humid.
- Very humid air prevents the evaporative cooling of sweaty or wet skin.
Water
- Swamp coolers require a constant supply of water to wet the pads.
- Water high in mineral content will leave mineral deposits on the pads and interior of the cooler. Water softeners, bleed-off and refill systems may relieve this problem, however.
- Water line needs protection against freeze bursting during off season, winter temperatures.
Miscellaneous
- Pollen, odors, and other outdoor contaminants may be blown into the building unless sufficient filtering is in place.
- The vents that allow air to exit the building may pose a physical security risk.
- Asthma patients may need to avoid evaporatively cooled environments.
See also
External links
- Swamp Cooler FAQ (http://www.air-n-water.com/faq_swamp.htm)
- USA Today's Wonderquest (http://www.usatoday.com/news/science/wonderquest/2001-08-22-swamp-coolers.htm)simple:Swamp cooler